Image sensor

ABSTRACT

An image sensor including a semiconductor substrate having a first surface and a second surface; and a pixel isolation film extending from the first surface of the semiconductor substrate into the semiconductor substrate and defining active pixels in the semiconductor substrate, wherein the pixel isolation film includes a buried conductive layer including polysilicon containing a fining element at a first concentration; and an insulating liner between the buried conductive layer and the semiconductor substrate, and wherein the fining element includes oxygen, carbon, or fluorine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application based on pending application Ser. No.16/451,412, filed Jun. 25, 2019, the entire contents of which is herebyincorporated by reference.

Korean Patent Application No. 10-2018-0135331, filed on Nov. 6, 2018, inthe Korean Intellectual Property Office, and entitled: “Image Sensors,”is incorporated by reference herein in its entirety.

BACKGROUND 1. Field

Embodiments relate to an image sensor.

2. Description of the Related Art

An image sensor is a device that converts an optical image signal intoan electric signal. The image sensor may include pixel region includinga plurality of photodiode regions in which incident light is receivedand converted into the electrical signal, and a pixel isolation regionfor electrically separating pixels from each other.

SUMMARY

The embodiments may be realized by providing an image sensor including asemiconductor substrate having a first surface and a second surface; anda pixel isolation film extending from the first surface of thesemiconductor substrate into the semiconductor substrate and definingactive pixels in the semiconductor substrate, wherein the pixelisolation film includes a buried conductive layer including polysiliconcontaining a fining element at a first concentration; and an insulatingliner between the buried conductive layer and the semiconductorsubstrate, and wherein the fining element includes oxygen, carbon, orfluorine.

The embodiments may be realized by providing an image sensor including asemiconductor substrate; and a pixel isolation film in a pixel trenchpassing through the semiconductor substrate and defining active pixelsin the semiconductor substrate, wherein the pixel isolation filmincludes an insulating liner on a sidewall of the pixel trench; and aburied conductive layer filled in an inside of the pixel trench on theinsulating liner, the buried conductive layer including polysiliconcontaining a fining element at a first concentration, and wherein thefining element includes oxygen, carbon, or fluorine.

The embodiments may be realized by providing an image sensor including asemiconductor substrate including a plurality of active pixels; and apixel isolation film between active pixels of the plurality of activepixels and in a pixel trench passing through the semiconductorsubstrate, wherein the pixel isolation film includes: an insulatingliner on a sidewall of the pixel trench; and a buried conductive layerfilled in an inside of the pixel trench on the insulating liner, theburied conductive layer including polysilicon containing a finingelement at a first concentration, and wherein the fining elementincludes oxygen and the first concentration is about 5 at % to about 40at %.

BRIEF DESCRIPTION OF THE DRAWINGS

Features will be apparent to those of skill in the art by describing indetail exemplary embodiments with reference to the attached drawings inwhich:

FIG. 1 illustrates a layout view of an image sensor according to exampleembodiments;

FIG. 2 illustrates a cross-sectional view taken along line II-II′ ofFIG. 1;

FIG. 3 illustrates an equivalent circuit diagram of an active pixel ofan image sensor according to example embodiments;

FIG. 4 illustrates a cross-sectional view of an image sensor accordingto example embodiments;

FIG. 5 illustrates a cross-sectional view of an image sensor accordingto example embodiments;

FIG. 6 illustrates a cross-sectional view of an image sensor accordingto example embodiments;

FIGS. 7A-7L illustrate cross-sectional views of stages in a method ofmanufacturing an image sensor according to example embodiments

FIG. 8 illustrates a flowchart of a method of manufacturing an imagesensor according to example embodiments;

FIGS. 9A-9C illustrate cross-sectional views of stages in a method ofmanufacturing an image sensor according to example embodiments;

FIG. 10 illustrates a flow chart of a method of manufacturing an imagesensor in accordance with example embodiments;

FIG. 11 illustrates a flowchart of a method of manufacturing an imagesensor according to example embodiments;

FIGS. 12A-12D illustrate cross-sectional views of stages in a method ofmanufacturing an image sensor according to example embodiments;

FIG. 13 illustrates a flow chart of a method of manufacturing an imagesensor in accordance with example embodiments;

FIG. 14 illustrates a flowchart of a method of manufacturing an imagesensor according to example embodiments; and

FIG. 15 illustrates an X-ray diffraction analysis graph of a buriedconductive layer included in an image sensor according to an Example andComparative Examples.

DETAILED DESCRIPTION

FIG. 1 illustrates a layout diagram of an image sensor 100 according toexample embodiments. FIG. 2 illustrates a cross-sectional view takenalong line II-II′ of FIG. 1.

Referring to FIGS. 1 and 2, the image sensor 100 may include an activepixel region APR, a peripheral circuit region PCR, and a pad region PDRin or on a semiconductor substrate 110.

The active pixel region APR may include a plurality of active pixels PXand each of a plurality of photoelectric conversion regions 120 may bearranged in each of the plurality of active pixels PX. In the activepixel region APR, a plurality of active pixels PX may be arranged in amatrix shape in the form of rows and columns along first direction (forexample, X direction in FIG. 1) parallel to an upper surface of thesemiconductor substrate 110 and second direction (for example, Ydirection in FIG. 1) parallel to the upper surface of the semiconductorsubstrate 110.

In an implementation, as illustrated, the peripheral circuit region PCRmay be on one side of the active pixel region APR in a plan view. In animplementation, the peripheral circuit region PCR may surround anentirety of the active pixel region APR. In an implementation, unlikethat shown in FIG. 1, the peripheral circuit region PCR may be on anadditional substrate, and then the additional substrate may be attachedto the semiconductor substrate 110.

The peripheral circuit region PCR may be a region where various kinds ofcircuits for controlling a plurality of active pixels PX in the activepixel region APR are formed. For example, the peripheral circuit regionPCR may include a plurality of transistors, and the plurality oftransistors may be driven to provide a constant signal in eachphotoelectric conversion region 120 of the active pixel region APR, orto control an output signal from each of the photoelectric conversionregion 120. In an implementation, the transistor may configure variouslogic circuits, such as a timing generator, a row decoder, a row driver,a correlated double sampler CDS, an analog to digital converter ADC, alatch, a column decoder, and the like.

The pad region PDR may surround the active pixel region APR and theperipheral circuit region PCR. A conductive pad PAD may be on theperipheral region of the semiconductor substrate 110 and may beelectrically connected to circuits in the plurality of active pixels PXand the peripheral circuit region PCR. The conductive pad PAD mayfunction as a connection terminal for externally supplying power andsignals to a circuit included in the plurality of active pixels PX andthe peripheral circuit region PCR.

The semiconductor substrate 110 may include a first surface 110F1 and asecond surface 110F2 opposing to each other. Herein, for convenience,the surface of the semiconductor substrate 110 on which a microlens 168is arranged is referred to as the second surface 110F2, and the surfaceopposite to the second surface 110F2 is referred to as the first surface110F1.

In an implementation, the semiconductor substrate 110 may include aP-type semiconductor substrate. For example, the semiconductor substrate110 may be a P-type silicon substrate. In an implementation, thesemiconductor substrate 110 may include a P-type bulk substrate and aP-type or a N-type epitaxial layer grown thereon. In an implementationts, the semiconductor substrate 110 may include an N-type bulk substrateand a P-type or an N-type epitaxial layer grown thereon. In animplementation, the semiconductor substrate 110 may be formed of anorganic plastic substrate.

A plurality of active pixels PX may be arranged in a matrix form in thesemiconductor substrate 110 in the active pixel region APR. One of thephotoelectric conversion regions 120 may be arranged in each of theplurality of active pixels PX. Each of the plurality of photoelectricconversion regions 120 may include a photodiode region 122 and a wellregion 124.

A pixel isolation film 130 may be in the semiconductor substrate 110 inthe active pixel region APR, and the plurality of active pixels PX maybe defined by the pixel isolation film 130. The pixel isolation film 130may be between one of the plurality of photoelectric conversion regions120 and another one of the photoelectric conversion regions 120 adjacentthereto. The one of the photoelectric conversion regions 120 and theother one of the photoelectric conversion regions 120 adjacent theretomay be physically and electrically separated by the pixel isolation film130. The pixel isolation film 130 may be between each of the pluralityof photoelectric conversion regions 120 arranged in a matrix form andmay have a grid or mesh shape in a plan view.

The pixel isolation film 130 may be in a pixel trench 130T passingthrough the semiconductor substrate 110 from the first surface 110F1 tothe second surface 110F2 of the semiconductor substrate 110. The pixelisolation film 130 may include an insulating liner 132 conformallyformed on a sidewall of the pixel trench 130T and a buried conductivelayer 134 filled in an inside of the pixel trench 130T on the insulatingliner 132.

In an implementation, the insulating liner 132 may include a metaloxide, e.g., hafnium oxide, aluminum oxide, tantalum oxide, or the like.In an implementation, the insulating liner 132 may serve as a negativefixed charge layer. In an implementation, the insulating liner 132 mayinclude an insulating material, e.g., silicon oxide, silicon nitride,silicon oxynitride, or the like.

The buried conductive layer 134 may include polysilicon that contains afining element at a first concentration. The fining element may include,e.g., oxygen, carbon, or fluorine. As used herein, the term “or” is notan exclusive term, e.g., the fining element may include one or more ofthe enumerated elements. In an implementation, the buried conductivelayer 134 may include polysilicon containing oxygen at a concentrationof about 5 at % (atomic percent) to about 40 at %. In an implementation,the buried conductive layer 134 may include polysilicon containingoxygen at a concentration of about 20 at % to about 30 at %. In animplementation, the buried conductive layer 134 may include polysiliconcontaining carbon at a concentration of about 1 at % to about 20 at %.In an implementation, the buried conductive layer 134 may includepolysilicon containing fluorine at a concentration of about 1 at % toabout 20 at %. In an implementation, the buried conductive layer 134 mayinclude a plurality of grains made of silicon and having a siliconcrystal structure, and the fining element may be uniformly dispersedwithin the grains of silicon. For example, the buried conductive layer134 may have a diffraction peak at about 28.44° represented by a silicon(111) crystal plane in an X-ray diffraction analysis.

The buried conductive layer 134 may include a polysilicon containing thefining element at the first concentration, and the buried conductivelayer 134 may have a relatively small grain size. In an implementation,the buried conductive layer 134 may have an average grain size of about30 nanometers (nm) or less. In an implementation, in the buriedconductive layer 134, a full width at half maximum of an X-raydiffraction peak (the peak being observed at a scattering angle of about28.44°) by the silicon (111) crystal plane observed in the X-raydiffraction analysis may be about 0.4° to about 1.1° (See FIG. 15). Inan implementation, the average grain size of the buried conductive layer134 calculated from the X-ray diffraction peak may be about 7.5 nm toabout 20.5 nm.

In an implementation, the pixel trench 130T may have a first width w11at the same level as the first surface 110F1 of the semiconductorsubstrate 110 and a second width w12 (that is smaller than the firstwidth w11) at the same level as the second surface 110F2 of thesemiconductor substrate 110. For example, the first width w11 of thepixel trench 130T measured (e.g., in the first or X direction) at thefirst surface 110F1 of the semiconductor substrate 110 may be greaterthan the second width w12 of the pixel trench 130T measured at thesecond surface 110F2 of the semiconductor substrate 110. In animplementation, the pixel trench 130T may have a first height h11 in adirection (e.g., Z direction) perpendicular to the first surface 110F1of the semiconductor substrate 110, and a ratio of the first height h11to the first width w11 may be about 20 to about 100.

In an implementation, voids or seams may not be formed within the buriedconductive layer 134. The pixel trench 130T may have a relatively highaspect ratio (e.g., an aspect ratio of about 20 to 100), and seams couldotherwise be formed in the conductive layer 134 in the process offorming the buried conductive layer 134 using polysilicon inside thepixel trench 130T, and undesired voids could be formed in the buriedconductive layer 134 due to grain growth or grain coalescence in theburied conductive layer 134 in a subsequent heat treatment processes.However, according to the example embodiments, the buried conductivelayer 134 may include the polysilicon containing the fining element(e.g., oxygen, carbon, or fluorine), and the buried conductive layer 134may be formed to have a relatively small grain size in the process offorming the buried conductive layer 134 filling an interior of the pixeltrench 130T. In addition, in a heat treatment process after theformation of the buried conductive layer 134, the fining element may beable to help restrain grain growth or grain coalescence, which couldotherwise occur due to the migration of silicon atoms, thereby voids orseams not being formed in the buried conductive layer 134. The grainsize and microstructure of the buried conductive layer 134 will bedescribed again in detail below with reference to FIG. 15.

The buried conductive layer 134 may not fill a portion of an interior ofthe pixel trench 130T and a bottom surface of the buried conductivelayer 134 may be at a level higher than the first surface 110F1 of thesemiconductor substrate 110 (e.g., the bottom surface of the buriedconductive layer 134 may be inwardly spaced apart from the first surface110F1 of the semiconductor substrate 110 by a predetermined distancealong the vertical direction (Z direction)). A buried insulating layer140 may fill a remaining portion of the pixel trench 130T on the bottomsurface of the buried conductive layer 134 and the insulating liner 132may be between the buried insulating layer 140 and an inner wall of thepixel trench 130T. In an implementation, an upper, lower, or outersurface of the buried insulating layer 140 may be at the same level as(e.g., coplanar with) the first surface 110F1 of the semiconductorsubstrate 110. In an implementation, the buried insulating layer 140 maybe omitted and the buried conductive layer 134 may be filled in aninside of the pixel trench 130T through the entire height h11 of thepixel trench 130T, such that the bottom or lower surface of the buriedconductive layer 134 may be at the same level as (e.g., coplanar with)the first surface 110F1 of the semiconductor substrate 110.

In an implementation, as shown in FIG. 2, an isolation film STI (whichdefines an active region) and a floating diffusion region FD may be onthe first surface 110F1 of the semiconductor substrate 110.

Gate electrodes TG, RG, SG (see FIG. 3) constituting a part of aplurality of transistors may be on the first surface 110F1 of thesemiconductor substrate 110. In an implementation, the plurality oftransistors may include a transmission transistor TX configured totransmit the charge generated in the photoelectric conversion region 120to the floating diffusion region FD, a reset transistor RX configured toperiodically reset the charge stored in the floating diffusion regionFD, a drive transistor DX configured to function as a source followerbuffer amplifier and to buffer a signal according to the charge chargedin the floating diffusion region, and a selection transistor SX forswitching and addressing in relation to selecting the active pixelregion APR.

In an implementation, as illustrated in FIG. 2, the transmission gate TGconstituting the transmission transistor TX may be a recess gate typeextending from the first surface 110F1 of the semiconductor substrate110 into the semiconductor substrate 110. In an implementation, atransmission gate insulating layer TGI may be between the semiconductorsubstrate 110 and the transmission gate TG. For example, as thetransmission gate TG is formed in the recess gate type, a portion of thetransmission gate insulating layer TGI may extend into the interior ofthe semiconductor substrate 110.

A first interconnection structure 152 may be on the first surface 110F1of the semiconductor substrate 110. The first interconnection structure152 may be electrically connected to the gate electrodes or the activeregion. The first interconnection structure 152 may be formed as astacked structure of a plurality of layers. The first interconnectionstructure 152 may include at least one of impurity-doped or undopedpolysilicon, metal, metal silicide, metal nitride, or metal-containingfilm. For example, the first interconnection structure 152 may includetungsten, aluminum, copper, tungsten silicide, titanium silicide,tungsten nitride, titanium nitride, doped polysilicon, and the like.

A first interlayer insulating film 154 may cover the firstinterconnection structure 152 on the first surface 110F1 of thesemiconductor substrate 110. The first interlayer insulating film 154may include an insulating material such as silicon oxide, siliconnitride, silicon oxynitride, or the like.

A rear insulating layer 160 may be arranged on the second surface 110F2of the semiconductor substrate 110. The rear insulating layer 160 may bearranged on substantially the entire area of the second surface 110F2 ofthe semiconductor substrate 110, and the rear insulating layer 160 maycontact an upper surface of the pixel isolation film 130 at the samelevel as the second surface 110F2 of the semiconductor substrate 110. Inan implementation, the rear insulating layer 160 may include a metaloxide such as hafnium oxide, aluminum oxide, tantalum oxide, or thelike. In an implementation, the rear insulating layer 160 may include aninsulating material such as silicon oxide, silicon nitride, siliconoxynitride, or a low dielectric constant material, or the like.

A guide pattern 162 may be on the rear insulating layer 160. In a planview, the guide pattern 162 may have a grid shape or a mesh shape. Theguide pattern 162 may help prevent incident light with a tilt angle withrespect to one photoelectric conversion region 120, from entering thephotoelectric conversion region 120. The guide pattern 162 may includeat least one metallic material, e.g., tungsten, aluminum, titanium,ruthenium, cobalt, nickel, copper, gold, silver or platinum.

A passivation layer 164 may cover the rear insulating layer 160 and theguide pattern 162 on the second surface 110F2 of the semiconductorsubstrate 110. A color filter 166 and a microlens 168 may be on thepassivation layer 164.

In an implementation, a supporting substrate 170 may be on the firstsurface 110F1 of the semiconductor substrate 110. An adhesive member maybe further arranged between the supporting substrate 170 and the firstinterlayer insulating film 154.

In the process of forming the buried conductive layer 134 usingpolysilicon inside the pixel trench 130T having a relatively high aspectratio, it is possible that a seam could be formed in the buriedconductive layer 134, and in a subsequent heat treatment process graingrowth or grain coalescence could occur to form an undesired void in theburied conductive layer 134. If such a void were to be formed,performance of the image sensor 100 may be lowered, due to an occurrenceof a dark current or an increase in noise level, or the like.

On the other hand, in the image sensor 100 according to an embodiment,the buried conductive layer 134 may include polysilicon containing thefining element (e.g., oxygen, carbon, or fluorine), and the buriedconductive layer 134 may be formed to have a relatively small grainsize. In addition, the fining element may help prevent grain growth orgrain coalescence in the heat treatment process after the formation ofthe buried conductive layer 134, and the formation of undesired voidsmay be prevented. For example, voids or seams may not be formed in theburied conductive layer 134, and the image sensor 100 may be preventedfrom generating a dark current or increasing of noise level to haveimproved performance.

FIG. 15 illustrates an X-ray diffraction analysis graph of the buriedconductive layer included in the image sensors according to an Exampleand Comparative Examples.

The following Example and Comparative Examples are provided in order tohighlight characteristics of one or more embodiments, but it will beunderstood that the Example and Comparative Examples are not to beconstrued as limiting the scope of the embodiments, nor are theComparative Examples to be construed as being outside the scope of theembodiments. Further, it will be understood that the embodiments are notlimited to the particular details described in the Example andComparative Examples.

Referring to FIG. 15, a buried conductive layer EX11 according to anExample was formed using polysilicon containing oxygen as the finingelement at a first concentration, as described with reference to FIGS. 1and 2, and then a subsequent heat treatment was performed. Buriedconductive layers CO11 and CO12 according to Comparative Examples 1 and2, respectively, were formed using polysilicon without the finingelement, and then a subsequent heat treatment was performed.

Referring to FIG. 15 and the following Table 1, in the buried conductivelayer EX11 according to the Example and the buried conductive layersCO11 and CO12 according to the Comparative Examples, diffraction peaksby silicon (111) crystal planes are observed at a scattering angle ofabout 28.44°, and the intensity of the diffraction peak of the buriedconductive layer EX11 according to the Example was lower than theintensity of the diffraction peaks of the buried conductive layers CO11and CO12 according to the Comparative Examples.

In addition, a full width at half maximum (FEX11) by the silicon (111)crystal plane of the buried conductive layer EX11 according to theExample was higher than a full width at half maximum FCO11 of the buriedconductive layer CO11 according to Comparative Example 1 and a fullwidth at half maximum FCO12 of the buried conductive layer CO12according to Comparative Example 2. From the calculation based on thefull widths at half maximum of such X-ray diffraction peaks, the buriedconductive layer EX11 according to the Example may have an average grainsize of about 16.8 nm, while the buried conductive layer CO11 accordingto the Comparative Example 1 may have an average grain size of about43.5 nm, and the buried conductive layer CO12 according to theComparative Example 2 may have an average grain size of about 45.8 nm.

TABLE 1 Intensity of (111) Full width at plane diffraction peak halfmaximum Comparative Example 1 (CO11) 481 0.19 Comparative Example 2(CO12) 611 0.18 Example (EX11) 79 0.49

Voids or seams were observed inside the buried conductive layers CO11and CO12 according to the Comparative Examples, while voids or seamswere not observed inside the buried conductive layer EX11 according tothe Example.

According to an embodiment, the buried conductive layer 134 (see FIG. 2)may have a relatively small grain size by including the fining element(including at least one of oxygen, carbon, and fluorine), and then theformation of undesired voids in a subsequent heat treatment process maybe prevented by the fining element.

FIG. 3 illustrates an equivalent circuit diagram of the active pixel PXof the image sensor 100 of FIGS. 1 and 2 according to exampleembodiments.

Referring to FIG. 3, the plurality of active pixels PX may be arrangedin a matrix form. Each of the plurality of active pixels PX may includea transmission transistor TX and logic transistors RX, SX, DX. Herein,the logic transistors may include a reset transistor RX, a selectiontransistor SX, and a drive transistor DX (or a source followertransistor). The reset transistor RX may include a reset gate RG and theselection transistor SX may include a selection gate SG and the transfertransistor TX may include a transmission gate TG.

Each of the plurality of active pixels PX may further include aphotoelectric conversion device PD and a floating diffusion region FD.The photoelectric conversion device PD may correspond to thephotoelectric conversion region 120 described with reference to FIGS. 1and 2. The photoelectric conversion device PD may generate andaccumulate photo charges in proportion to the amount of incident lightfrom an outside, and a photodiode, a photo transistor, a photo gate, apinned photodiode PPD and combinations thereof may be used as thephotoelectric conversion device PD.

The transmission gate TG may transfer the charges generated in thephotoelectric conversion device PD to the floating diffusion region FD.The floating diffusion region FD may receive the charges generated inthe photoelectric conversion device PD and accumulate the charges. Thedrive transistor DX may be controlled according to the amount of thephoto charges accumulated in the floating diffusion region FD.

The reset transistor RX may periodically reset the charges accumulatedin the floating diffusion region FD. A drain electrode of the resettransistor RX is connected to the floating diffusion region FD and asource electrode thereof is connected to a power source voltage VDD.When the reset transistor RX is turned on, the power source voltage VDDconnected to the source electrode of the reset transistor RX istransferred to the floating diffusion region FD. When the resettransistor RX is turned on, the charges accumulated in the floatingdiffusion region FD are discharged to reset the floating diffusionregion FD.

The drive transistor DX is connected to a current source (not shown)located outside the plurality of active pixels PX and then functions asa source follower buffer amplifier, and it amplifies potential change inthe floating diffusion region FD and outputs it to the output line VOUT.

The selection transistor SX may select the plurality of active pixels PXrow by row and when the selection transistor SX is turned on, the powersupply voltage VDD may be transferred to a source electrode of the drivetransistor DX.

FIG. 4 illustrates a cross-sectional view of an image sensor 100Aaccording to example embodiments. FIG. 4 is a cross-sectional view of aportion corresponding to the portion II-II′ of FIG. 1. In FIG. 4, thesame reference numerals as in FIGS. 1 to 3 denote the same elements.

Referring to FIG. 4, the pixel isolation layer 130A may include aninsulating liner 132 and a buried conductive layer 134A. The buriedconductive layer 134A may contain polysilicon containing the finingelement at the first concentration and a P-type dopant at a secondconcentration or an N-type dopant at the second concentration. Forexample, the fining element may include oxygen, carbon, or fluorine. Inan implementation, the P-type dopant may include, e.g., boron, aluminum,or indium. In an implementation, the N-type dopant may include, e.g.,phosphorus, arsenic, or antimony. The fining element may function as anadditive, with which the buried conductive layer 134A may be formed tohave a fine grain size, and the P type dopant or the N type dopant mayhelp increase the conductivity of the buried conductive layer 134A.

In an implementation, the fining elements may be uniformly dispersed inthe buried conductive layer 134A, and the P-type dopant or the N-typedopant may also be uniformly dispersed in the buried conductive layer134A.

In the manufacturing process of the image sensor 100A according to anembodiment, a first conductive layer 134A1 (see FIG. 9A) may be formedby using polysilicon containing the P-type dopant or the N-type dopanton an inner wall of the pixel trench 130T, a second conductive layer134B1 (see FIG. 9B) may be formed on the first conductive layer 134A1 byusing the polysilicon containing the fining element, and the buriedconductive layer 134A may be formed by performing a heat treatmentprocess and then diffusing the fining element in the first conductivelayer 134A1 and the P-type or the N-type dopant in the second conductivelayer 134B1.

FIG. 5 illustrates a cross-sectional view of an image sensor 100Baccording to example embodiments. FIG. 5 is a cross-sectional view takenalong line II-II′ of FIG. 1. In FIG. 5, the same reference numerals asin FIGS. 1 to 4 denote the same elements.

Referring to FIG. 5, a pixel isolation film 130B may include aninsulating liner 132, a buried conductive layer 134B, and an interfacelayer 136B. The buried conductive layer 134B may include polysiliconcontaining the fining element at a first concentration, and the finingelement may include at least one of oxygen, carbon, and fluorine.

The interface layer 136B may be between the insulating liner 132 and theburied conductive layer 134B. The interface layer 136B may includepolysilicon containing the P-type dopant or the N-type dopant.

In an implementation, the interface layer 136B may be between the rearinsulating layer 160 and the buried conductive layer 134B at the samelevel as the second surface 110F2 of the semiconductor substrate 110, sothat the buried conductive layer 134B may not contact the rearinsulating layer 160. In an implementation, the interface layer 136B maysurround the sidewall of the buried conductive layer 134B on thesidewall of the pixel trench 130T, so that both the buried conductivelayer 134B and the interface layer 136B may be in contact with the rearinsulating layer 160 at the same level as the second surface 110F2 ofthe semiconductor substrate 110.

In the manufacturing process of the image sensor 100B according to theexample embodiments, the first conductive layer 134A1 (see FIG. 9A) mayformed on the inner wall of the pixel trench 130T by using polysiliconcontaining the P-type dopant or the N-type dopant, and then a secondconductive layer 134B1 (see FIG. 9B) may be formed on the firstconductive layer 134A1 by using polysilicon containing the finingelement. Herein, a part of the first conductive layer 134A1 maycorrespond to the interface layer 136B and a part of the secondconductive layer 134B1 may correspond to the buried conductive layer134B, respectively.

FIG. 6 illustrates a cross-sectional view of an image sensor 100Caccording to example embodiments. FIG. 6 is a cross-sectional view of aportion corresponding to the portion II-II′ of FIG. 1. In FIG. 6, thesame reference numerals as in FIGS. 1 to 5 denote the same elements.

Referring to FIG. 6, a pixel isolation film 130C may include aninsulating liner 132, a buried conductive layer 134C, and an interfacelayer 136C. The buried conductive layer 134C may include polysiliconcontaining the fining element at a first concentration, and the finingelement may include at least one of oxygen, carbon, and fluorine.

The interface layer 136C may be between the insulating liner 132 and theburied conductive layer 134C, and may have a tapered shape in adirection (e.g., Z direction) toward a first surface 110F1 of thesemiconductor substrate 110. For example, a width of the interface layer136C may become smaller in the Z direction from the second surface 110F2to the first surface 110F1 of the semiconductor substrate 110. Theinterface layer 136C may include polysilicon containing a P-type dopantor an N-type dopant.

In the manufacturing process of the image sensor 100C according to theexample embodiments, a first conductive layer 134A2 (see FIG. 12A) maybe formed on an inner wall of the pixel trench 130T by using polysiliconcontaining the P-type dopant or the N-type dopant. And then, byperforming anisotropic etching to the first conductive layer 134A2, atop portion 134A2T of the first conductive layer 134A2 (see FIG. 12B)may have the tapered shape while a top entrance of the pixel trench 130Tmay be expanded. Thereafter, a second conductive layer 134B2 (see FIG.12C) may be formed on the first conductive layer 134A2 using polysiliconcontaining the fining element. Herein, a part of the first conductivelayer 134A2 may correspond to the interface layer 136C and a part of thesecond conductive layer 134B2 may correspond to the buried conductivelayer 134C, respectively.

FIGS. 7A-7L illustrate cross-sectional views of stages in a method ofmanufacturing the image sensor 100 in accordance with exampleembodiments. In FIGS. 7A-7L, cross-sectional views corresponding to thecross-sectional views taken along line II-II′ of FIG. 1 are shown in theorder of process. In FIGS. 7A-7L, the same reference numerals as inFIGS. 1-6 denote the same elements.

Referring to FIG. 7A, the semiconductor substrate 110 having the firstsurface 110F1 and the second surface 110F2 opposite to each other isprovided.

Thereafter, a first mask layer 210 having an opening 210H may be formedon the first surface 110F1 of the semiconductor substrate 110 and usingthe first mask layer 210, a part of the semiconductor substrate 110 maybe removed from the first surface 110F1 to form an isolation trench ST.

Referring to FIG. 7B, an isolation insulating layer 220 may be formed onthe first surface 110F1 of the semiconductor substrate 110 and the firstmask layer 210 to fill the isolation trench ST. The isolation insulatinglayer 220 may be formed using silicon oxide, silicon oxynitride, orsilicon nitride.

Thereafter, a mask pattern may be formed on the isolation insulatinglayer 220, and the pixel trench 130T may be formed in the semiconductorsubstrate 110 using the mask pattern.

The pixel trench 130T may have a first height h01 from the first surface110F1 of the semiconductor substrate 110 and may have a first width w11along a first direction (an X direction) at the same level as the firstsurface 110F1 of the semiconductor substrate 110. In an implementation,the pixel trench 130T may have an aspect ratio of about 20 to about 100.

In an implementation, the pixel trench 130T may have a second width w13(that is less than the first width w11 along the first direction (the Xdirection)) at a bottom portion 130TB of the pixel trench 130T. In thiscase, a sidewall 130TS of the pixel trench 130T may be slightly inclinedso that the width of the pixel trench 130T becomes narrower from the topto the bottom of the pixel trench 130T.

Referring to FIG. 7C, a preliminary insulating liner 132P may beconformally formed on the isolation insulating layer 220 and the innerwall of the pixel trench 130T by a chemical vapor deposition (CVD)process, or an atomic layer deposition (ALD) process. The preliminaryinsulating liner 132P may have substantially the same thickness on thesidewall 130TS and the bottom portion 130TB of the pixel trench 130T.

Referring to FIG. 7D, a conductive layer 134P filling the inner of thepixel trench 130T may be formed on the preliminary insulating liner132P. The conductive layer 134P may include polysilicon containing thefining element at a first concentration.

In an implementation, the process of forming the conductive layer 134Pmay include the CVD process or the ALD process using a silicon sourcematerial and the fining element source material as precursors. In animplementation, when the fining element includes oxygen, the finingelement source material may include, e.g., an oxidizing agent such asnitrogen oxide (N₂O) or nitrogen monoxide (NO). In an implementation,when the fining element includes carbon, the fining element sourcematerial may include, e.g., hydrocarbons such as methane (CH₄), ethylene(C₂H₄), acetylene (C₂H₂) or propane (C₃H₈). In an implementation, whenthe fining element includes fluorine, the fining element source materialmay include, e.g., a fluorine-containing precursor material such asnitrogen trifluororide (NF₃), silicon tetrafluoride (SiF₄), etc.

For example, the conductive layer 134P may be formed by reactionaccording to the following Formula 1 using a silicon source material andan oxygen source material.

SiH₄(g)+N₂O→Si(s)+O+2H₂(g)+N₂(g)  Formula 1

In an implementation, the conductive layer 134P may include polysiliconcontaining about 5 at % to 40 at % of oxygen. In an implementation, whenthe fining element includes carbon or fluorine, the conductive layer134P may include polysilicon containing about 1 at % to 20 at % ofcarbon or polysilicon containing about 1 at % to 20 at % of fluorine.

The conductive layer 134P may be formed to include polysiliconcontaining the fining element at the first concentration, and theconductive layer 134P may have a relatively small grain size. Forexample, the conductive layer 134P may have polycrystallinemicrostructure having an average grain size of less than about 30 nm. Inan implementation, voids or seams may not be formed within theconductive layer 134P in the pixel trench 134T having a relatively largeaspect ratio.

Referring to FIG. 7E, a portion of the conductive layer 134P (see FIG.7D) on the preliminary insulating liner 132P outside the pixel trench134T may be removed to remain the buried conductive layer 134 in thepixel trench 134T. In an implementation, as shown in FIG. 7E, the topsurface of the buried conductive layer 134 may be at a lower level thanthe first surface 110F1 of the semiconductor substrate 110.

Referring to FIG. 7F, a preliminary buried insulating layer 140P may beformed on the buried conductive layer 134 and the preliminary insulatingliner 132P using an insulating material. The preliminary buriedinsulating layer 140P may fill the remaining space of the pixel trench130T.

Referring to FIG. 7G, a portion of the preliminary buried insulatinglayer 140P (see FIG. 7F), a portion of the preliminary insulating liner132P (see FIG. 7F), a portion of the isolation insulating layer 220 andthe first mask layer 210 (see FIG. 7F) may be removed to expose thefirst surface 110F1 of the semiconductor substrate 110. A remainingportion of the preliminary buried insulating layer 140P may be theburied insulating layer 140, a remaining portion of the preliminaryinsulating liner 132P may be the insulating liner 132 and a remainingportion of the isolation insulating layer 220 may be the isolation filmSTI.

Referring to FIG. 7H, a photoelectric conversion region 120 including aphotodiode region 122 and a well region 124 may be formed from or at thefirst surface 110F1 of the semiconductor substrate 110 by an ionimplantation process. For example, the photodiode region 122 may beformed by doping with N-type impurities, and the well region 124 may beformed by doping with P-type impurities.

A gate structure including a transmission gate TG and a transmissiongate insulating layer TGI may be formed on the first surface 110F1 ofthe semiconductor substrate 110 and then a floating diffusion region FDand an active region may be formed in a part of the first surface 110F1of the semiconductor substrate 110 by the ion implantation process.

Referring to FIG. 7I, a first interconnection structure 152 and a firstinterlayer insulating film 154 covering the first interconnectionstructure 152 may be formed on the semiconductor substrate 110 byrepeatedly performing the operations of forming a conductive layer onthe first surface 110F1 of the semiconductor substrate 110, patterningthe conductive layer, and forming an insulating layer covering thepatterned conductive layer.

Thereafter, a supporting substrate 170 may be adhered to the firstinterlayer insulating film 154. An adhesive layer may be between thesupporting substrate 170 and the first interlayer insulating film 154.

Referring to FIG. 7J, the semiconductor substrate 110 may be invertedsuch that the second surface 110F2 of the semiconductor substrate 110faces upward. Herein, the bottom portion 130TB of the pixel trench 130Tmay not be exposed at the second surface 110F2.

Referring to FIG. 7K, a portion of the semiconductor substrate 110 maybe removed from or at the second surface 110F2 of the semiconductorsubstrate 110 by a planarization process such as a CMP process or anetch-back process until the buried conductive layer 134 is exposed. Asthe removal process is performed, the level of the second surface 110F2of the semiconductor substrate 110 may be lowered.

One active pixel PX surrounded by the pixel isolation film 130 may bephysically and electrically separated from the active pixel PX adjacentthereto. The pixel trench 130T extends from the first surface 110F1 tothe second surface 110F2 of the semiconductor substrate 110 and may havea first height h11 along the vertical direction, the Z direction. In animplementation, the first height h11 of the pixel trench 130T after theplanarization process may be smaller than the first height h01 (see FIG.7B) of the pixel trench 130T prior to the planarization process. In animplementation, the first height h11 of the pixel trench 130T after theplanarization process may be substantially identical to the first heighth01 of the pixel trench 130T before the planarization process.

Thereafter, a rear insulating layer 160 may be formed on the secondsurface 110F2 of the semiconductor substrate 110, the buried conductivelayer 134, and the insulating liner 132. The rear insulating layer 160may be formed using an insulating material such as a metal oxide such ashafnium oxide, aluminum oxide, tantalum oxide, or the like, siliconoxide, silicon nitride, silicon oxynitride, or a low-k material.

Referring to FIG. 7L, a conductive layer may be formed on the rearinsulating layer 160, and the conductive layer may be patterned to forma guide pattern 162. The guide pattern 162 may overlap the pixelisolation film 130 in the active pixel region APR.

Thereafter, a conductive pad PAD (see FIG. 1) may be formed on the rearinsulating layer 160 in the pad region PDR. The conductive pad PAD maybe formed by sequentially forming a first metal layer and a second metallayer. For example, the first metal layer may be formed using the metalmaterial such as titanium, titanium nitride, tantalum, tantalum nitride,titanium tungsten, tungsten, aluminum, cobalt, nickel or copper by a CVDprocess, an ALD process or the like. The second metal layer may beformed using the metal material such as tungsten, aluminum, cobalt,nickel, or copper by a CVD process, an ALD process, a plating process,or the like.

Thereafter, a passivation layer 164 may be formed on the rear insulatinglayer 160 and the guide pattern 162 and a color filter 166 and amicrolens 168 may be formed on the passivation layer 164.

The image sensor 100 may be completed by the above-described process.

According to the method of manufacturing the image sensor according tothe above-described example embodiments, the buried conductive layer 134may be formed using polysilicon containing the fining element, and voidsor seams may not be formed in the buried conductive layer 134. Further,even though the heat treatment process is further performed, the finingelement included in the buried conductive layer 134 may suppress themovement of silicon atoms or inhibit grain growth, and therefore theformation of voids or seams may be prevented inside the buriedconductive layer 134.

FIG. 8 illustrates a flowchart of a method of manufacturing the imagesensor 100 according to the example embodiments. FIGS. 9A to 9Cillustrate cross-sectional views of stages in a method of manufacturingthe image sensor 100 according to the example embodiments. FIG. 8 andFIGS. 9A to 9C, the same reference numerals as in FIGS. 1 to 7L denotethe same elements.

First, the process described with reference to FIGS. 7A to 7C may beperformed to form a preliminary insulating liner 132P inside the pixeltrench 130T.

Referring to FIGS. 8 and 9A, a first conductive layer 134A1 includingpolysilicon may be formed on an inner wall of the pixel trench 130T(operation S210). The first conductive layer 134A1 may includepolysilicon that is free of impurities or fining elements.

In an implementation, the first conductive layer 134A1 may be formed bya reaction according to the following Formula 2 using a silicon sourcematerial.

SiH₄(g)→Si(s)+2H₂(g)  Formula 2

Referring to FIGS. 8 and 9B, a second conductive layer 134B1 includingpolysilicon containing fining elements may be formed on the firstconductive layer 134A1 to fill an interior of the pixel trench 130T(operation S220).

In an implementation, when the fining element includes oxygen, thesecond conductive layer 134B1 may be formed using a silicon sourcematerial and an oxygen source material by the reaction according toFormula 1 below.

SiH₄(g)+N₂O→Si(s)+O+2H₂(g)+N₂(g)  Formula 1

Referring to FIGS. 8 and 9C, the semiconductor substrate 110 may beheat-treated, e.g., annealed (operation S230). The fining elementcontained in the second conductive layer 134B1 may be diffused into thefirst conductive layer 134A1 by the heat treatment process, to therebyform a conductive layer 134P1.

In an implementation, the process for forming the first conductive layer134A1 and the process for forming the second conductive layer 134B1 maybe performed in-situ within the same chamber or reactor. In animplementation, the process for forming the first conductive layer 134A1and the process for forming the second conductive layer 134B1 may beperformed ex-situ in different chambers or reactors.

In an implementation, as illustrated in FIGS. 8 and 9A to 9C, the secondconductive layer 134B1 may be formed to fill the pixel trench 130T. Inan implementation, the first conductive layer 134A1 and the secondconductive layer 134B1 having a relatively thin thickness may bealternately and repeatedly formed on the inner wall of the pixel trench130T. For example, the processes of forming the first conductive layer134A1 and the second conductive layer 134B1 may be repeated n times tofill the inside of the pixel trench 130T.

Thereafter, the image sensor 100 may be completed by performing theprocesses described with reference to FIGS. 7E to 7L.

FIG. 10 illustrates a flowchart of a method of manufacturing the imagesensor 100 according to the example embodiments.

Referring to FIG. 10 together with FIG. 9A, a first conductive layer134A1 containing polysilicon containing fining elements may be formed onthe inner wall of the pixel trench 130T (operation S210A).

Referring to FIG. 10 together with FIG. 9B, a second conductive layer134B1 including polysilicon not containing the fining elements orimpurities may be formed on the first conductive layer 134A1 to fill theinside of the pixel trench 130T (operation S220A).

Referring to FIG. 10 together with FIG. 9C, the semiconductor substrate110 may be heat-treated (operation S230A). The fining elements includedin the first conductive layer 134A1 may be diffused into the secondconductive layer 134B1 by the heat treatment process to form theconductive layer 134P1.

FIG. 11 illustrates a flowchart of stages in a method of manufacturingthe image sensor 100 according to the example embodiments. FIGS. 12A to12D illustrate cross-sectional views of stages in a method ofmanufacturing the image sensor 100 according to example embodiments.

First, the process described with reference to FIGS. 7A to 7C isperformed to form a preliminary insulating liner 132P inside the pixeltrench 130T.

Referring to FIGS. 11 and 12A, a first conductive layer 134A2 includingpolysilicon may be formed on an inner wall of the pixel trench 130T(operation S210B). The first conductive layer 134A2 may includepolysilicon that is free of impurities or fining elements.

Referring to FIGS. 11 and 12B, an anisotropic etching process may beperformed on the first conductive layer 134A2 (operation S215B). Aportion of the first conductive layer 134A2 on the preliminaryinsulating liner 132P on the first surface 110F1 of the semiconductorsubstrate 110 and a portion of the first conductive layer 134A2 on thebottom portion 130TB of the pixel trench 130T may be removed by theanisotropic etching process. The first conductive layer 134A2 may remainon a sidewall 130TS of the pixel trench 130T and a top portion 134A2T ofthe first conductive layer 134A2 may remain and may have a tapered shapein a direction (Z direction) toward the first surface 110F1 of thesemiconductor substrate 110 (e.g., in the direction toward an entranceof the pixel trench 130T). As the top portion 134A2T of the firstconductive layer 134A2 has a tapered shape, the entrance of the pixeltrench 130T may expand laterally as compared to the bottom of the pixeltrench 130T.

Referring to FIGS. 11 and 12C, a second conductive layer 134B2 includingpolysilicon containing the fining elements may be formed on the firstconductive layer 134A2 to fill the inside of the pixel trench 130T(operation S220B).

As the entrance of the pixel trench 130T expands laterally as comparedto the bottom of the pixel trench 130T, the source material may besmoothly supplied to the inside of the pixel trench 130T in the processof forming the second conductive layer 134B2. Thus, the secondconductive layer 134B2 may densely fill the inside of the pixel trench130T without voids or seams.

Referring to FIGS. 11 and 12D, the semiconductor substrate 110 may beheat-treated, e.g., annealed (operation S230B). The fining elementsincluded in the second conductive layer 134B2 may be diffused into thefirst conductive layer 134A2 by the heat treatment process to form theconductive layer 134P2.

In an implementation, the process for forming the first conductive layer134A2, the process for anisotropically etching the first conductivelayer 134A2, and the process for forming the second conductive layer134B2 may be performed in-situ in a same chamber or reactor. In animplementation, the process for forming the first conductive layer134A2, the process for anisotropically etching the first conductivelayer 134A2, and the process for forming the second conductive layer134B2 may be performed ex-situ in different chambers or reactors.

In an implementation, as illustrated in FIGS. 11 and 12A to 12D, thesecond conductive layer 134B2 may include polysilicon containing thefining elements. In an implementation, the first conductive layer 134A2may include polysilicon containing the fining elements and the secondconductive layer 134B2 may include polysilicon that does not contain thefining elements or impurities.

In an implementation, as illustrated in FIGS. 11 and 12A to 12D, thesecond conductive layer 134B2 may fill the pixel trench 130T. In animplementation, on the inner wall of the pixel trench 130T, the firstconductive layer 134A2 and the second conductive layer 134B2 having arelatively thin thickness may be alternately and repeatedly formed. Forexample, the process of forming the first conductive layer 134A2, theanisotropic etching process of the first conductive layer 134A2, theprocess of forming the second conductive layer 134B2, and theanisotropic etching process of the second conductive layer 134B2 arerepeated n times, and finally, the first conductive layer 134A2 may beformed to fill the inside of the pixel trench 130T.

Thereafter, the image sensor 100 may be completed by performing theprocesses described with reference to FIGS. 7E to 7L.

FIG. 13 illustrates a flowchart of a method of manufacturing the imagesensor 100A according to the example embodiments.

Referring to FIG. 13 together with FIG. 9A, a first conductive layer134A1 including polysilicon containing dopant at a second concentrationmay be formed on the inner wall of the pixel trench 130T (operationS210C). The dopant may include the N-type dopant or the P-type dopant.

In an implementation, the first conductive layer 134A1 may be formed byreactions according to Formula 3 or Formula 4 using the silicon sourcematerial and the dopant source material.

SiH₄(g)+PH₃→Si(s)+P+H₂(g)  Formula 3

SiH₄(g)+BCl₃→Si(s)+B+H₂(g)+Cl₂(g)  Formula 4

Referring to FIG. 13 together with FIG. 9B, a second conductive layer134B1 including polysilicon containing fining elements at the firstconcentration may formed on the first conductive layer 134A1, to therebyfill the inside of the pixel trench 130T (operation S220C).

Referring to FIG. 13 together with FIG. 9C, the semiconductor substrate110 may be heat-treated (operation S230C). The dopant contained in thefirst conductive layer 134A1 may be diffused into the second conductivelayer 134B1 by the heat treatment process and the fining elementscontained in the second conductive layer 134B1 may be diffused into thefirst conductive layer 134A1, so that the conductive layer 134P1 may beformed.

Thereafter, the image sensor 100A including the buried conductive layer134A may be completed by performing the processes described withreference to FIGS. 7E to 7L.

In an implementation, as illustrated in FIG. 13, the dopant and thefining elements may be uniformly dispersed in the entire region of theburied conductive layer 134A by performing the heat treatment process.In an implementation, the heat treatment process of the semiconductorsubstrate 110 may be omitted and the first conductive layer 134A1portion may be remained as the interface layer 136B and the secondconductive layer 134B1 portion may be remained as the buried conductivelayer 134B. In this case, the image sensor 100B described with referenceto FIG. 5 may be formed.

FIG. 14 illustrates a flowchart of a method of manufacturing the imagesensor 100A according to the example embodiments.

Referring to FIG. 14 together with FIG. 12A, a first conductive layer134A2 including polysilicon containing dopants at the secondconcentration may be formed on the inner wall of the pixel trench 130T(operation S210D). The dopant may include the N-type dopant or theP-type dopant.

Referring to FIG. 14 together with FIG. 12B, an anisotropic etchingprocess may be performed on the first conductive layer 134A2 (operationS215D). The first conductive layer 134A2 may remain on the sidewall130TS of the pixel trench 130T by the anisotropic etching process andthe entrance of the pixel trench 130T may be further expanded laterallyas compared to the bottom of the pixel trench 130T.

Referring to FIG. 14 together with FIG. 12C, a second conductive layer134B2 including polysilicon containing fining elements at a firstconcentration may be formed on the first conductive layer 134A2 tothereby fill the inside of the pixel trench 130T (operation S220D).

Referring to FIG. 14 together with FIG. 12D, the semiconductor substrate110 may be heat-treated (operation S230D). The dopants contained in thefirst conductive layer 134A2 may be diffused into the second conductivelayer 134B2 by the heat treatment process and the fining elementscontained in the second conductive layer 134B2 may be diffused into thefirst conductive layer 134A2, so that the conductive layer 134P2 may beformed.

Thereafter, the image sensor 100A including the buried conductive layer134A may be completed by performing the processes described withreference to FIGS. 7E to 7L.

In an implementation, as illustrated in FIG. 14, the dopants and thefining elements may be uniformly dispersed in the entire region of theburied conductive layer 134A by performing the heat treatment process.In an implementation, the heat treatment process of the semiconductorsubstrate 110 may be omitted and the portion of the first conductivelayer 134A2 may be remained as the interface layer 136C and the portionof the second conductive layer 134B2 may remain as the buried conductivelayer 134C. In this case, the image sensor 100C described with referenceto FIG. 6 may be formed.

By way of summation and review, as a degree of integration of the imagesensor increases, a size of each of the plurality of photodiode regionsmay be reduced. A degree of difficulty of a process for forming thepixel isolation region may increase.

One or more embodiments may provide an image sensor including aphotodiode.

One or more embodiments may provide an image sensor that may fill aburied conductive layer without voids or seams in a pixel isolationregion having a large aspect ratio.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation. In someinstances, as would be apparent to one of ordinary skill in the art asof the filing of the present application, features, characteristics,and/or elements described in connection with a particular embodiment maybe used singly or in combination with features, characteristics, and/orelements described in connection with other embodiments unless otherwisespecifically indicated. Accordingly, it will be understood by those ofskill in the art that various changes in form and details may be madewithout departing from the spirit and scope of the present invention asset forth in the following claims.

What is claimed is:
 1. An image sensor, comprising: a semiconductorsubstrate having a first surface and a second surface opposing the firstsurface; and a pixel isolation film in a pixel trench extending from thefirst surface of the semiconductor substrate into the semiconductorsubstrate, the pixel isolation film defining active pixels in thesemiconductor substrate, wherein the pixel isolation film includes: aninsulating liner on an inner wall of the pixel trench; an interfacelayer on the insulating liner in the pixel trench, the interface layerhaving a first end and a second end, the first end of the interfacelayer being closer to the first surface than the second end of theinterface layer; and a buried layer on the interface layer and fillingan inside the pixel trench, and wherein the first end of the interfacelayer has a first width, the second end of the interface has a secondwidth, and the second width is greater than the first width.
 2. Theimage sensor as claimed in claim 1, wherein the interface layer includespolysilicon containing a P-type dopant or an N-type dopant.
 3. The imagesensor as claimed in claim 2, wherein the P-type dopant consists ofboron.
 4. The image sensor as claimed in claim 1, wherein a bottomsurface of the buried layer is in contact with the second surface of thesemiconductor substrate.
 5. The image sensor as claimed in claim 1,wherein: the buried layer includes polysilicon containing a finingelement, the fining element consists of oxygen, carbon, or fluorine,when the fining element consists of oxygen, a concentration of oxygen inthe buried layer is 6 at % to 40 at %, when the fining element consistsof carbon, a concentration of carbon in the buried layer is 6 at % to 20at %, and when the fining element consists of fluorine, a concentrationof fluorine in the buried layer is about 1 at % to about 20 at %.
 6. Theimage sensor as claimed in claim 1, wherein: the buried layer furtherincludes a P-type dopant or an N-type dopant, the P-type dopant includesboron, aluminum, or indium, and the N-type dopant includes phosphorus,arsenic, or antimony.
 7. The image sensor as claimed in claim 1, whereinthe interface layer has a tapered shape in a direction from the secondsurface of the semiconductor substrate toward the first surface of thesemiconductor substrate.
 8. The image sensor as claimed in claim 1,wherein: the buried layer has an average grain size of about 30 nm orless, and the buried layer has a full width at half maximum of an X-raydiffraction peak by a silicon (111) crystal plane observed in an X-raydiffraction analysis of about 0.4° to about 1.1°.
 9. The image sensor asclaimed in claim 1, further comprising: an interconnection structure onthe first surface of the semiconductor substrate; and a microlens on thesecond surface of the semiconductor substrate, wherein the pixelisolation film extends from the first surface to the second surface ofthe semiconductor substrate and passes through the semiconductorsubstrate.
 10. The image sensor as claimed in claim 1, wherein the pixeltrench has a first width at a same level as the first surface of thesemiconductor substrate and a second width that is smaller than thefirst width at a same level as the second surface.
 11. The image sensoras claimed in claim 10, wherein a ratio of a first height in a directionperpendicular to the first surface with respect to the first width isabout 20 to about
 100. 12. The image sensor as claimed in claim 1,wherein no seams or voids are arranged within the buried layer.
 13. Animage sensor, comprising: a semiconductor substrate having a firstsurface and a second surface opposing the first surface; and a pixelisolation film in a pixel trench extending from the first surface of thesemiconductor substrate into the semiconductor substrate, the pixelisolation film defining active pixels in the semiconductor substrate,wherein the pixel isolation film includes: an insulating liner on aninner wall of the pixel trench; an interface layer on the insulatingliner in the pixel trench, the interface layer having a first end and asecond end, the first end of the interface layer being closer to thefirst surface than the second end of the interface layer; and a buriedlayer on the interface layer and filling an inside the pixel trench, andwherein the first end of the interface layer has a tapered shape towardthe first surface of the semiconductor substrate.
 14. The image sensoras claimed in claim 13, wherein the interface layer includes polysiliconcontaining a P-type dopant or an N-type dopant.
 15. The image sensor asclaimed in claim 14, wherein the P-type dopant consists of boron. 16.The image sensor as claimed in claim 13, wherein a bottom surface of theinterface layer is in contact with second surface of the semiconductorsubstrate.
 17. The image sensor as claimed in claim 13, wherein: theburied layer includes polysilicon containing a fining element, thefining element consists of oxygen, carbon, or fluorine, when the finingelement consists of oxygen, a concentration of oxygen in the buriedlayer is 6 at % to 40 at %, when the fining element consists of carbon,a concentration of carbon in the buried layer is 6 at % to 20 at %, andwhen the fining element consists of fluorine, a concentration offluorine in the buried layer is about 1 at % to about 20 at %.
 18. Theimage sensor as claimed in claim 13, wherein: the buried layer furtherincludes a P-type dopant or an N-type dopant, the P-type dopant includesboron, aluminum, or indium, and the N-type dopant includes phosphorus,arsenic, or antimony.
 19. The image sensor as claimed in claim 13,wherein the first end of the interface layer has a first width, thesecond end of the interface has a second width, and the second width isgreater than the first width.
 20. The image sensor as claimed in claim13, wherein: the buried layer has an average grain size of about 30 nmor less, and the buried layer has a full width at half maximum of anX-ray diffraction peak by a silicon (111) crystal plane observed in anX-ray diffraction analysis of about 0.4° to about 1.1°.